netdev - Re: [PATCH] Remove unused function parameter in __smc_diag

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Message-ID: <538b7781-0d57-45e6-a00a-fb03c0c30a52@linux.ibm.com>
Date: Tue, 12 Nov 2024 08:36:13 +0100
From: Wenjia Zhang <wenjia@...ux.ibm.com>
To: Manas <manas18244@...td.ac.in>
Cc: Jan Karcher <jaka@...ux.ibm.com>, "D. Wythe" <alibuda@...ux.alibaba.com>,
        Tony Lu <tonylu@...ux.alibaba.com>, Wen Gu <guwen@...ux.alibaba.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
        Shuah Khan <shuah@...nel.org>, Anup Sharma <anupnewsmail@...il.com>,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Remove unused function parameter in __smc_diag_dump



On 11.11.24 16:10, Manas wrote:
> On 11.11.2024 15:11, Wenjia Zhang wrote:
>>
>>
>> On 09.11.24 07:28, Manas via B4 Relay wrote:
>>> From: Manas <manas18244@...td.ac.in>
>>>
>>> The last parameter in __smc_diag_dump (struct nlattr *bc) is unused.
>>> There is only one instance of this function being called and its passed
>>> with a NULL value in place of bc.
>>>
>>> Signed-off-by: Manas <manas18244@...td.ac.in>
>>> ---
>>> The last parameter in __smc_diag_dump (struct nlattr *bc) is unused.
>>> There is only one instance of this function being called and its passed
>>> with a NULL value in place of bc.
>>>
>>> Though, the compiler (gcc) optimizes it. Looking at the object dump of
>>> vmlinux (via `objdump -D vmlinux`), a new function clone
>>> (__smc_diag_dump.constprop.0) is added which removes this parameter from
>>> calling convention altogether.
>>>
>>> ffffffff8a701770 <__smc_diag_dump.constprop.0>:
>>> ffffffff8a701770:       41 57                   push   %r15
>>> ffffffff8a701772:       41 56                   push   %r14
>>> ffffffff8a701774:       41 55                   push   %r13
>>> ffffffff8a701776:       41 54                   push   %r12
>>>
>>> There are 5 parameters in original function, but in the cloned function
>>> only 4.
>>>
>>> I believe this patch also fixes this oops bug[1], which arises in the
>>> same function __smc_diag_dump. But I couldn't verify it further. Can
>>> someone please test this?
>>>
>>> [1] https://syzkaller.appspot.com/bug?extid=271fed3ed6f24600c364
>>> ---
>>>  net/smc/smc_diag.c | 6 ++----
>>>  1 file changed, 2 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/net/smc/smc_diag.c b/net/smc/smc_diag.c
>>> index 
>>> 6fdb2d96777ad704c394709ec845f9ddef5e599a..8f7bd40f475945171a0afa5a2cce12d9aa2b1eb4 100644
>>> --- a/net/smc/smc_diag.c
>>> +++ b/net/smc/smc_diag.c
>>> @@ -71,8 +71,7 @@ static int smc_diag_msg_attrs_fill(struct sock *sk, 
>>> struct sk_buff *skb,
>>>  static int __smc_diag_dump(struct sock *sk, struct sk_buff *skb,
>>>                 struct netlink_callback *cb,
>>> -               const struct smc_diag_req *req,
>>> -               struct nlattr *bc)
>>> +               const struct smc_diag_req *req)
>>>  {
>>>      struct smc_sock *smc = smc_sk(sk);
>>>      struct smc_diag_fallback fallback;
>>> @@ -199,7 +198,6 @@ static int smc_diag_dump_proto(struct proto 
>>> *prot, struct sk_buff *skb,
>>>      struct smc_diag_dump_ctx *cb_ctx = smc_dump_context(cb);
>>>      struct net *net = sock_net(skb->sk);
>>>      int snum = cb_ctx->pos[p_type];
>>> -    struct nlattr *bc = NULL;
>>>      struct hlist_head *head;
>>>      int rc = 0, num = 0;
>>>      struct sock *sk;
>>> @@ -214,7 +212,7 @@ static int smc_diag_dump_proto(struct proto 
>>> *prot, struct sk_buff *skb,
>>>              continue;
>>>          if (num < snum)
>>>              goto next;
>>> -        rc = __smc_diag_dump(sk, skb, cb, nlmsg_data(cb->nlh), bc);
>>> +        rc = __smc_diag_dump(sk, skb, cb, nlmsg_data(cb->nlh));
>>>          if (rc < 0)
>>>              goto out;
>>>  next:
>>>
>>> ---
>>> base-commit: 59b723cd2adbac2a34fc8e12c74ae26ae45bf230
>>> change-id: 20241109-fix-oops-__smc_diag_dump-06ab3e9d39f4
>>>
>>> Best regards,
>>
>> That's true that the last parameter is not used. And the patch you 
>> suggested as a cleanup patch looks good to me. However, it should not 
>> fix the bug[1], because it does not match what the bug[1] described. 
>> Thank you, Jeongjun, for testing it! That verified that it indeed 
>> didn't fix the issue. I think the root cause is on handling 
>> idiag_sport. I'll look into it.
>>
>> [1] https://syzkaller.appspot.com/bug?extid=271fed3ed6f24600c364
>>
>> Thanks,
>> Wenjia
> 
> Thank you Wenjia for reviewing this.
> 
> Should I make any changes to the commit message if we are going forward 
> with it
> being as a cleanup patch? The commit message itself (barring the cover 
> letter)
> should be enough, I reckon.
> 
I think it is ok as it is.

Thanks,
Wenjia